Global warming is a result of the increase in concentration of greenhouse gases (GHGs) in the atmosphere. GHGs selectively absorb infrared radiation and re-emit it back to the atmosphere, thereby heating the earth's surface. GHGs include carbon dioxide (76%), methane (13%), nitrous oxide (6%) and fluorocarbons (5%). Monitoring of these gases is important for the control of global warming and facilitates carbon trading strategies being implemented by the international community.
Current technologies for GHG monitoring include optical spectroscopy and gas chromatography (GC). The optical spectroscopy method includes Fourier transform infrared (FTIR) and cavity ring down (CRD) spectroscopy. These are inherently complex and expensive instruments in which quantification of multiple species with low concentration is difficult. Meanwhile, the GC analysis of some GHGs is cost-effective and provides high resolution separation for diverse components; however, the monitoring of trace levels of GHG species such as methane and chlorofluorocarbons (CFCs) remains a challenge. While the concentration of CO2 is relatively high and does not require additional preconcentration, the concentration of organic species, namely methane and others such as the chlorofluorocarbon (CFCs) is of particular importance where preconcentration is necessary. Since methane is the most volatile of the GHGs, it follows that if one can preconcentrate CH4, one can analyze all other greenhouse gases of interest. Similarly, other air pollutants including volatile and semivolatile organics are also of interest.
A microtrap is a capillary tubing packed with a sorbent for analyte retention, along with the capability of rapid desorption. Microtraps have been fabricated from microbore capillary as well as via silicon micromachining D. J. Butcher, Microchem. J., 66 (2000) 55. Their small dimension allows rapid desorption of adsorbed compounds, with potential advantages of faster operation, smaller bandwidth and low detection limit. Consequently, they are ideal for detectors such as photo ionization and flame ionization detectors and in conjunction with micro gas chromatography (GC). Microtraps are used for sample delivery to analytical instruments when preconcentration is required. A microtrap may serve as an integrated concentration-injection device. See, S. Mitra et al., J. Chromatogr. A 736 (1996) 165-173; A. Kroupa et al., J. Chromatogr. A 1038 (2004) 215; J. Pollmann et al., J. Chromatogr. A 1134 (2006) 1. Sorbent selection is important because the analytes need to be retained in a small quantity of sorbent for rapid, quantitative detection. J. Yin et al., Opt. Commun. 20 (2002) 99; C. H. Hussain et al., J. Chromatogr. A 1185 (2008)161.
To date, there is no commercially available preconcentrator for the greenhouse gases of interest. Accordingly, it would be advantageous to provide a microtrap for preconcentration of GHGs of interest such as methane and CFCs so that GHG monitoring of these, as well as other air pollutants, can be carried out at low concentrations.